1. Field of the Invention
This invention relates to a light transmitting device for use in a viewing or optical apparatus, particularly an optical device that enables a viewer to observe objects at night or under low-light conditions.
2. Description of Related Art
Night vision devices are widely used in the military to provide soldiers, aviators, and sailors with the ability to view objects at night or under low light conditions. A typical night vision device contains many optical components including an image intensifier tube and several lens elements that comprise the objective lens assembly, the collimator lens assembly, the diopter lens assembly, and the eyepiece assembly. Each of the optical elements must be precisely spaced and aligned to meet the optical performance requirements of the device.
The image intensifier tube converts visible and infrared energy into visible light. By receiving small quantities of both visible and non-visible near infrared light reflected off objects on the ground, the image intensifier amplifies the small quantities into visible light. The conversion typically requires sophisticated power supplies and circuitry to control the operation of the image intensifier tube and the sophisticated optical arrangements that direct the visible and infrared energy into the image intensifier tube.
The night vision device can be a self-contained transportable unit powered by batteries. The batteries are disposable or rechargeable and are preferably widely available. As a consequence of the power needed for operation of the device, batteries often need to be changed or recharged. When the power produced by the batteries is low, the viewing device cannot operate properly. Thus, it is important for the user to know when to replace batteries in the device, particularly when uninterrupted maximum night viewing operation is desired. It is also important to the user to know when the infrared illuminator is in operation.
ITT Corporation, the assignee herein, manufactures many night vision devices having various applications. Visible indicators such as LEDs are located in the field of view in these viewing devices. Several of these devices are discussed below.
U.S. Pat. No. 5,683,831 to Baril et al. describes a compact battery pack for a helmet mounted night vision device. The circuitry is designed to detect reduced voltage from one of the battery sets. The signal to the user is sent through a shielded cable to a small LED which is positioned within the user's field of view. When the LED flashes, this indicates that the batteries of the selected battery set are in need of replacement.
U.S. Pat. No. 5,537,261 to Palmer describes night vision binoculars having an LED disposed in the diopter cell assembly which is continually visible to the user. The LED is coupled to the CPU and lights when the power supply is drained, thereby indicating to the viewer that the batteries are low.
U.S. Pat. No. 5,157,553 to Phillips, et al., describes a collimator for a binocular viewing system. In the single objective lens arrangement, a single source image is viewed and the light from the image is divided into two separate corresponding optical outputs for binocular viewing. This is accomplished by a collimator lens assembly, a beam splitter, and two diopter cell assemblies. The collimator lens assembly re-images a source image at a substantially infinite conjugate. The rays of light leaving the collimator lens assembly are substantially parallel. The parallel light is then evenly divided by the beam splitter and directed toward the diopter cell assemblies. Diopter cell assemblies provide optical power to the split beam path, and direct the split image into two eyepiece lens assemblies by utilizing a mirror or prism.
Diopter cell assemblies can include an LED. The purpose of the LED is to superimpose a signal light over the image being viewed. For instance, a small light is superimposed over the viewed image to indicate to a viewer that the battery is low in the assembly or to indicate that an ancillary infrared light source has been turned on. The LED is typically positioned within the diopter cell assembly behind an elliptical mirror. A hole drilled into the back surface of the mirror allows light from an LED to pass through the material of the mirror. The manufacture and assembly of such a device is costly.
U.S. Pat. No. 5,347,397 to Nelson et al. describes a diopter cell assembly for a binocular viewing system having a single objective lens arrangement. The diopter cell assembly reorients an optical image from a first optical pathway to a second optical pathway. An LED is positioned over a transparent segment of a flat mirror to produce a superimposed image over the image being redirected by the diopter cell assembly, thus avoiding the problem of creating an elliptical mirror, aligning and adhesively attaching the mirror. A small aperture formed in the reflective surface of a mirror is located directly below the region of the LED. The aperture allows light from an LED to pass through the mirror and be viewed.
Of interest to the present invention is U.S. Pat. No. 5,594,254 to Palmer, assigned to ITT Corporation, the assignee of the present invention. Palmer describes an illuminator device for use with night vision devices. The device is coupled to a tripod mount and allows the user to adjust the direction of a beam of light projected by the illuminator relative to the line of sight of the night vision apparatus. The illuminator can be an LED or a laser light source.
The problem of the present viewing devices is that none can transmit light from a visible indicator located outside the field of view to a location inside the field of view of an apparatus at a desired optical location. Up to now, the devices had visible indicators located within the field of view of the user.
Thus, there remains a need for a device that transmits light from one or more visible indicators outside the field of view of the user for transferring into the field of view at desired optical locations, indicating to the viewer that the power supply is low, or that the infrared illuminator is in operation, while maintaining clearly-separated signals that can be unambiguously interpreted by the user.